Preventing pressure ulcers by pressure distribution via a liquid crystal elastomer Smart Skin

Pressure Ulcers (PU) are skin injuries costing an estimated 26 billion dollars per year. A sine qua non factor is prolonged pressure. Pressure from the body weight of hospitalized patients is enough to injure their skin and, without early action, can worsen and endanger patient life. One way to prevent pressure ulcers is to reduce the peak pressure on the skin to avoid ischemia. Liquid Crystal Elastomer (LCE) viscoelastic properties could make a Smart Skin, relieving pressure on the skin. To develop this Smart Skin, we will first explore the behavior of the skin under compression and, second, the behavior of the Smart Skin compressed by the weight of the body. In the first study, we aim at elucidating the link between mechanical loading and ischemia in the skin, considering the time-dependent properties of the skin. We model the skin microcirculation with a viscoelastic constitutive model and realistic blood vessels geometry to observe the impact of viscoelastic behavior on PU risk, quantified by a decrease in blood flow. A necessary condition to design a Smart Skin from novel LCEs is to predict their behavior reliably. In the second study, we developed and performed an experiment measuring the change in phase of the LCE under local compression. This experiment is then tentatively compared to a numerical simulation incorporating a dedicated constitutive model currently in development. These two approaches show the impact of time-dependence on the materials involved, whether biological or synthetic, in the decrease in blood flow and PU onset. They also show the impact of the nonlinearity of the LCE behavior on its behavior in compression